Pros and cons of HRV vs Fresh Air Ventilation in a dry heating/cooling climate.

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Great thread! I will, hopefully soon, be getting a CO2 monitor to measure my house. I have an ERV with a percent timer. I bet I am over ventilating a lot of the time.

Keep us posted. My guess is that you are over-ventilating during cold windy weather, about right during moderate weather, and under ventilating during warm calm. What part of the country are you in? How is your indoor dew point verses outside dew point or indoor %RH? How many occupants and sqft. of home?
Keep us posted.
Regards TB

I read an article somewhere that said they checked a bunch of homes and found that 77% were overventilated.

From what I've read so far. I think that without using some measure like CO2, the only way to insure enough ventilation is to overventilate part of the time. Seems kinda whacky to me, but that's what it appears.

Keep us posted. My guess is that you are over-ventilating during cold windy weather, about right during moderate weather, and under ventilating during warm calm. What part of the country are you in? How is your indoor dew point verses outside dew point or indoor %RH? How many occupants and sqft. of home?
Keep us posted.
Regards TB

NW Wisconsin.
2800 sq ft including conditioned basement.
Mom, dad, a 2 year old and 4 year old.

From what I am finding, you will save energy, moisture, and wear by not operating your erv when not occupied throughout the year. Also operating full time when occupied and calm winds/moderate temps provides better indoor air quality. The % timers under ventilate when you need the ventilation. You over-ventilate when unoccoupied and windy, cold weather. Better moisture conservation during extreme low outdoor dew points is the biggest benefit. 3-4 occupants are needed to keep a small home at comfortable moisture levels during low winter outdoor dew points. CO2 ventilation control does have benefit for automating the on/off control of any ventilation device. Most occupants will not deal with the daily adjustment needs for ideal ventilation schedules.
Regards TB

Getting back to my idea about "base ventilation". This is used in commercial buildings where there are non-occupant sources of CO2 that prevent the indoor CO2 level from returning to outside levels (~400PPM). In other words, the building always needs that much ventilation to return to "fresh air" CO2 levels even when not occupied. This allows sensors that use ABC (automatic background calibration) such as the Honeywell C7232A to calibrate properly. Using ABC, the sensor never needs manual calibration for the life of the sensor (~15 years).

OK, so that's for commercial, but we're talking about residential so why am I bring this up? Sensor ABC algorithms need the indoor CO2 to drop to outdoor levels at least once every 7 or 14 days, depending on the sensor. Checking my indoor CO2 levels, I see that when the house is unoccupied for a few hours, I never get to 400PPM. It does get to 600 or 700 occasionally, either when we're out for a few hours or when we're sleeping, or when it's really windy. So, I was thinking, why not use base ventilation to bring in a small amount of ventilation continually, to get the base level down closer to that of outdoor levels. In commercial, I have seen numbers like 20% or 25%.

So how would we do that in a home. What about controlling ventilation with a timer to provide 20-25% of the ASHRAE requirement, in parallel with a CO2 sensor that would fully open the vent? So, in other words, the house always gets 20% to 25%, but gets full ventilation if the sensor reaches the threshold (800, 1000, or 1200).

Panasonic has bath fans that ramp up and down based upon motion sensing. Put one in my GF's house, set continuous at 30, jumps to 80 or 100 when it senses.

My ERV has all kinds of settings, and a 15 minute high button in the bathroom. (She's not thrilled when I see the master control showing "high fan" and I shout "are you pooping?" She keeps a copy of Dale Carnegie on my bed-table, and I can almost hear her thinking "read the book a-hole!") :-)

Do you have a link to the product from Ultra Air that you talked about that controls ventilation by CO2 levels?

This is a custum control without support currently. Will become a fully supported control in a few months. From what I am seeing, If the space never gets below 600 ppm CO2, the control will read 450 when it is really 600. You set the control to activate at 600, this provides fresh air when occupied.
In addition, when you have active ventilation, the space may will be at 600 when you leave the space. Thus the space will go lower and readjust the sensors reading.
Also the ABC number and time is programable. This means you can determine the time and ppm. Currently we are using 450 and 2 weeks.
I have access to a limited number of custom DEH 3000 controllers with CO2 control of fresh air ventilation. I have some operating for upto 18 months of operation. Refinements a being made as we speak. I am using them on different types of ventilation systems like ERV, make-up, and exhaust systems.
Regards TB

This is a custum control without support currently. Will become a fully supported control in a few months. From what I am seeing, If the space never gets below 600 ppm CO2, the control will read 450 when it is really 600. You set the control to activate at 600, this provides fresh air when occupied.
In addition, when you have active ventilation, the space may will be at 600 when you leave the space. Thus the space will go lower and readjust the sensors reading.
Also the ABC number and time is programable. This means you can determine the time and ppm. Currently we are using 450 and 2 weeks.
I have access to a limited number of custom DEH 3000 controllers with CO2 control of fresh air ventilation. I have some operating for upto 18 months of operation. Refinements a being made as we speak. I am using them on different types of ventilation systems like ERV, make-up, and exhaust systems.
Regards TB

I think this will be a popular product. With the cost of CO2 sensors dropping, emphasis on energy conservation, and increased awareness of IAQ, having an integrated product should be a good thing.

Of course, it appears that you can combine a CO2 sensor with any type of ventilator and maybe accomplish "almost" the same thing.

Oh, and if one of the high-end thermostat manufacturers would add CO2 sensor input to one of their thermostats, well that would be excellent too.

I think this will be a popular product. With the cost of CO2 sensors dropping, emphasis on energy conservation, and increased awareness of IAQ, having an integrated product should be a good thing.

Of course, it appears that you can combine a CO2 sensor with any type of ventilator and maybe accomplish "almost" the same thing.

Oh, and if one of the high-end thermostat manufacturers would add CO2 sensor input to one of their thermostats, well that would be excellent too.

Here is an interesting point. The weather data for last year shows that you have high winds abount once per month. I am attaching the data. It show 20-30 mph winds occasionally. This level of wind will reduce the CO2 levels in a home signicantly. This is an opportunity to reset the meter more accurately. Between varible weather and opening the home, ABC calibration should be adequate. Also I found a plastic garbage bag of fresh air around the meter resets the ABC.
Regards TB
This is from wunderground.comHistory for Albuquerque NM.pdf